In 1976, both Viking 1 and Viking 2 touched down on the surface of Mars. Both landed on vast, flat plains, chosen because they were ideal locations for landing safely. Perhaps the most important Viking experiment for assessing whether life could exist on Mars was the gas chromatograph and mass spectrometer (GCMS) instrument, built by a team led by Klaus Biermann of MIT. Ultimately, Biermann and his GCMS team reported a definitive answer: “No organic compounds were found at either of the two landing sites.” None, nada, zilch.

This scientific discovery had enormous importance for our understanding Mars. Summing up what we learned from the Viking missions in 1992, and in particular what we learned from the absence of any organics in the sampled Martian soil, a team of Viking scientists wrote, “The Viking findings established that there is no life at the two landing sites.” Furthermore, because these two sites were thought to be extremely representative of all of Mars, they concluded that this result “virtually guarantees that the Martian surface is lifeless everywhere.”

If Mars is sterile, then SpaceX and NASA and Blue Origin and Mars One can all move forward with their efforts to land colonists on Mars in the near future. They needn’t wrestle with any ethical issues about contaminating Mars.

Fast forward a generation. In a paper published in Science last week, Jennifer Eigenbrode and her team, working with data collected by the Mars Science Laboratory (i.e., the Curiosity rover), report that they discovered organic molecules in Martian soil. The importance of this discovery for the possible existence of life on Mars is hard to overstate. The discovery of organics on Mars is a BIG deal.

Let’s be careful in discussing organic molecules. An organic molecule must contain at least one carbon atom and that carbon atom must be chemically bonded to a hydrogen atom. All life on Earth is built on a backbone (literally) of organic molecules (DNA). And life on Earth can produce organic molecules (for example, the methane that is produced in the stomachs of cows). But abiological processes can also make organic molecules. In fact, the universe is full of such molecules known as PAHs (polycyclic aromatic hydrocarbons), which are found in interstellar clouds and the atmospheres of red giant stars and which have absolutely nothing to do with life.

Repeat: the presence of organic molecules on Mars does not mean life has been found on Mars. The absence of organic molecules in the Martian soil, as discovered in the Viking experiments, however, almost certainly means “no life here.”

Were the Viking scientists wrong? Yes, in part. Their conclusion that the plains of Mars are representative of every locale on Mars was an overreach. When assessing whether the environment on Mars might be hospitable to life, local matters. That conclusion shouldn’t surprise anyone. After all, we find significant differences on Earth between the amount and kinds of life in the Mojave Desert and the Amazon River basin. Why? Water.

The vast, flat plains of Mars are free of organics, but they are unlike Gale Crater. Gale Crater was once a lake, full of water and dissolved minerals. We know now that certain locations on Mars that were warm and wet for extended periods of time in the ancient past have preserved a record of the organic molecules that formed in those environments.

Could life have played a role in creating these molecules? Maybe, but we don’t know, yet. We do know, however, where to keep looking. We do know where to send the next several generations of robots. We do know that we should build robotic explorers that can drill deep into the soil and explore caves in places similar to Gale Crater.

Abigail Allwood, working at NASA’s Jet Propulsion Laboratory, is building a detector called PIXL that will be sent to Mars on a rover mission that is scheduled for launch in 2020. PIXL will be able to make smart decisions, based on the chemistry of a rock, as to whether that rock sample might contain ancient, fossilized microbes. A later mission might retrieve Allwood’s PIXL specimens and bring them back to Earth for more sophisticated laboratory studies. With instruments like PIXL, we have a good chance of definitively answering the question, “Does Mars or did Mars ever have life?”

What does the presence of organic molecules in the Martian regolith mean, as discovered by Curiosity? Those molecules could mean that life is or once was present on Mars. Finding those molecules just raised the stakes in the search for life on Mars. The jury is still out, but the betting odds just changed.

Given all we currently know about Mars, should we be sending astronauts to Mars in the next decade? Do we have the right to contaminate Mars if is already home to native Martian microbes? These are important questions that are more relevant than ever.

Astronomer David A. Weintraub thinks it won’t be long before we are faced with this question not as a hypothetical, but as a real option. Based on the pace of research and the growing private interest in space exploration, humans might be considering trips to Mars before the next century.

In his new book Life on Mars: What to Know Before We Go, Weintraub argues that would-be colonizers of the red planet should first learn whether life already exists on Mars. Just as colonization of various parts of Earth has historically decimated human, animal, and plant populations, so, argues Weintraub, will human colonization of Mars dramatically affect and likely destroy any life that might already exist on Mars. Before we visit, we need to know what – and whom – we might be visiting.

While scientists have yet to determine whether life exists on the red planet, they agree that if Martians do exist, they probably aren’t little green men. So where does our popular idea of Martians come from? Artists and writers have been imagining and depicting Martian life in a variety of ways since long before space travel was a reality. Check out these descriptions of imagined Martian life from over one hundred years ago.

Cover of The Martian, by George du Maurier

In George du Maurier’s 1897 gothic science fiction story The Martian, Martians are described as furry amphibians who are highly skilled in metalworking and sculpting:

“Man in Mars is, it appears, a very different being from what he is here. He is amphibious, and descends from no monkey, but from a small animal that seems to be something between our seal and our sea-lion….

“His five senses are extraordinarily acute, even the sense of touch in his webbed fingers and toes….

“These exemplary Martians wear no clothes but the exquisite fur with which nature has endowed them, and which constitutes a part of their immense beauty….

“They feed exclusively on edible moss and roots and submarine seaweed, which they know how to grow and prepare and preserve. Except for heavy-winged bat-like birds, and big fish, which they have domesticated and use for their own purposes in an incredible manner (incarnating a portion of themselves and their consciousness at will in their bodies), they have cleared Mars of all useless and harmful and mutually destructive forms of animal life. A sorry fauna, the Martian—even at its best—and a flora beneath contempt, compared to ours.”

“How the Earth Men Learned the Martian Language,” from Edison’s Conquest of Mars by Garrett P. Serviss

In Garrett Serviss’s Edison’s Conquest of Mars (1898), on the other hand, Martians are huge creatures, two to three times as tall as a human:

“It is impossible for me to describe the appearance of this creature in terms that would be readily understood. Was he like a man? Yes and no. He possessed many human characteristics, but they were exaggerated and monstrous in scale and in detail. His head was of enormous size, and his huge projecting eyes gleamed with a strange fire of intelligence. His face was like a caricature, but not one to make the beholder laugh. Drawing himself up, he towered to a height of at least fifteen feet.”

Edwin Lester Arnold, in Lieut. Gullivar Jones: His Vacation, published in 1905, describes Martians instead as “graceful and slow,” with an “odor of friendly, slothful happiness about them”:

“They were the prettiest, daintiest folk ever eyes looked upon, well-formed and like to us as could be in the main, but slender and willowy, so dainty and light, both the men and the women, so pretty of cheek and hair, so mild of aspect, I felt, as I strode amongst them, I could have plucked them like flowers and bound them up in bunches with my belt. And yet somehow I liked them from the first minute; such a happy, careless, light-hearted race, again I say, never was seen before.”

“The old man sat and talked with me for hours,” from A Princess of Mars by Edgar Rice Burroughs

And in Edgar Rice Burroughs’ A Princess of Mars, published in 1917, Martians are finally depicted as the little green men of the popular imagination:

“Five or six had already hatched and the grotesque caricatures which sat blinking in the sunlight were enough to cause me to doubt my sanity. They seemed mostly head, with little scrawny bodies, long necks and six legs, or, as I afterward learned, two legs and two arms, with an intermediary pair of limbs which could be used at will either as arms or legs. Their eyes were set at the extreme sides of their heads a trifle above the center and protruded in such a manner that they could be directed either forward or back and also independently of each other, thus permitting this queer animal to look in any direction, or in two directions at once, without the necessity of turning the head.

“The ears, which were slightly above the eyes and closer together, were small, cup-shaped antennae, protruding not more than an inch on these young specimens. Their noses were but longitudinal slits in the center of their faces, midway between their mouths and ears.

“There was no hair on their bodies, which were of a very light yellowish-green color. In the adults, as I was to learn quite soon, this color deepens to an olive green and is darker in the male than in the female. Further, the heads of the adults are not so out of proportion to their bodies as in the case of the young.”

To learn more about Martians in popular culture, the history of planetary astronomy, and the scientific search for life on Mars, read David Weintraub’s Life on Mars!

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